Some prior art solutions for discharging material from the bottom of a silo employ a transport screw turning about the center axis of the silo and extending radially from the wall of the silo to a discharge opening in the center of the bottom. The turning movement can be brought about for example, as disclosed in Finnish patent specification no. 51325, by a hydraulic device disposed at the outer end of the transport screw and communicating with a geared step ring provided outside the silo.
Other prior art solutions for discharging material from the bottom of a silo have discharge arms fixed to a drive shaft disposed centrally in the silo which arms are arranged to move material to a discharge opening or openings of the silo while the shaft rotates. The discharge arms are arranged to be rotated continuously to the same direction or to be moved to and fro by a motor or a hydraulic device. An example of this kind of an apparatus is disclosed in Finnish patent specification no. 47328.
Finnish patent application no. FI 881926 discloses a discharge apparatus for a silo, comprising a double-ended discharge arm pivoted in an excentric pin of a drive shaft disposed centrally in the silo. The movement of the discharge arms is controlled by pins provided at the ends of the discharge arms and by pins disposed at the bottom portion of the silo by means of which rollers are caused to move, when the drive shaft rotates, along a substantially epicycloidal path around the pins thus forcing the discharge arm in a slow "sawing" turning movement.